1. Field of the Invention
The present invention is directed to a C-arm X-ray system having a C-arm that carries an X-ray source and a detector residing opposite one another at its ends, and that can be swiveled around the subject in multiple axes.
2. Description of the Prior Art
In addition to the swivel of the C-arm around an axis lying essentially horizontally in the plane of the C-armxe2x80x94angulationxe2x80x94, the C-arm also can swivel in its plane around an axis perpendicular theretoxe2x80x94referred to as orbital rotation.
Due to the properties of the commonly employed Feldkamp image reconstruction algorithm, only that part of a volume that is covered in each 2D projection in a graduated circle revolution can be calculated. Since the reconstruction algorithm is based on the principle of filtered back-projection, projections that are cut off in the filter direction should be avoided. For calculating thorax slices, for example, it is therefore necessary to employ a detector with dimensions large enough in one dimension (length) so as to completely cover the full width of the trunk of the body. The height of the detector determines how many axial slices can be calculated.
In practice, the reoccurring problem arises that, due to the detector residing stationarily opposite the X-ray source and with a limited positioning possibilities of the C-arm, projections that are more or less cut off and that negatively influence the reconstruction result are generated dependent on the subject position and the rotational sense. Moreover, volumes of different sizes are obtained, their size being dependent on whether an angulation or an orbital rotation is implemented. When the objective is for the subject to be imaged to be largely completely covered in the projection exposures in all rotational directions, then a quadratic detector must be employed, that may be unnecessarily large and that is correspondingly expensive.
An object of the present invention is to design a C-arm X-ray system of the type initially described wherein, despite a limited size of the detector surface, better image qualities can be achieved by avoiding clipped projections.
This object is inventively achieved in a C-arm system wherein the detector is mounted so as to be rotatable around the axis preceding therefrom to the X-ray source and/or to be displaceable parallel to the detector surface and/or along a arcuate path. The detector preferably has a rectangular detector surface and is pivotable by at least 90xc2x0 such that the long side can be aligned parallel to the rotational plane. Given an angulation, thus, the long side of the rectangular detector surface resides perpendicular to the plane of the C-arm, and, given orbital rotation, the long side of the detector surface lies parallel to the plane of the C-arm.
The displaceability of the detector parallel to the detector surface or along an arcuate path is particularly useful in instances wherein there is no isocenter for the orbital rotation or when the arrangement is undertaken such that a 360xc2x0 scan is possible.